Calibration verification by Monte-Carlo simulations of a total gamma counting tunnel for clearance purposes

The Joint Research Centre of Ispra is one of the research centres belonging to the European Commission, and was created in the late '50s, in order to steer European research on nuclear industry. It currently hosts numerous nuclear facilities, some of which are maintained in operation, while others were shutdown in the past years or are currently being decommissioned. The license for the waste station includes clearance for historical and post operations solid materials. As a license requirement for clearance, measurement and characterization of the material must be performed to verify that the radioactive concentration is below the established threshold levels given by the Italian Nuclear Safety Authority. The final survey on the potentially clearable material homogeneous lots is performed through a commercial total gamma counting tunnel composed by eight plastic scintillators. Calibration is obtained by a standard container through a set of calibration measurements. A verification, via Monte Carlo simulations, of the measurement method of the gamma counting tunnel has been performed in order to have complete reliability on the system used for verifying the radioactive activity in the potentially clearable materials.